Compare the relative stability of the following species and indicate the magnetic properties : ${{\rm{O}}_2}{\rm{,O}}_2^ + ,{\rm{O}}_2^ - $ (super oxide); ${\rm{O}}_2^{2 - }$ (Peroxide)

Electron configuration and bond order of $\mathrm{O}_{2}, \mathrm{O}_{2}^{+}, \mathrm{O}_{2}^{-}$:

Bond order of $\mathrm{O}_{2}$ :

In $\mathrm{O}_{2}, \mathrm{Z}=8 \mathrm{So}$, Total electron $=16$

Electron configuration in $MO$ for $\mathrm{O}_{2}:(\sigma 1 s)^{2}\left(\sigma^{*} 1 s\right)^{2}(\sigma 2 s)^{2}\left(\sigma^{*} 2 s\right)^{2}\left(\sigma 2 p_{z}\right)^{2}\left(\pi 2 p_{x}\right)^{2}\left(\pi 2 p_{y}\right)^{2}$

$\left(\pi^{*} 2 p_{x}\right)^{1}$ $\left(\pi^{*} 2 p_{y}\right)^{1}$

$\mathrm{BO}=\frac{1}{2}\left(\mathrm{~N}_{\mathrm{b}}-\mathrm{N}_{\mathrm{a}}\right)=\frac{1}{2}(10-6)=$ (Double bond)

Bond order of $\mathrm{O}_{2}^{+}$:

Total electron in $\mathrm{O}_{2}=16$ and total electron in

$\mathrm{O}_{2}^{+}=15$

Electron configuration in $MO$ for $\mathrm{O}_{2}:\left(\sigma_{1 s}\right)^{2}\left(\sigma_{1 s}^{*}\right)^{2}\left(\sigma_{2 s}\right)^{2}\left(\sigma_{2 s}^{*}\right)^{2}\left(\sigma_{2 p_{z}}\right)^{2}\left(\pi_{2 p_{x}}\right)^{2}$

$\left(\pi_{2 p_{y}}\right)^{2}\left(\pi_{2 p_{x}}^{*}\right)^{1}\left(\pi_{2 p_{y}}^{*}\right)^{0}$

$\mathrm{BO}=\frac{1}{2}\left(\mathrm{~N}_{\mathrm{b}}-\mathrm{N}_{\mathrm{a}}\right)=\frac{1}{2}(10-5)=2.5$

Bond order of $\mathrm{O}_{2}^{-}:$

Total electron in $\mathrm{O}_{2}^{-}=16+1=17$

Electron configuration in $MO$ for $\mathrm{O}_{2}^{-}:\left(\sigma_{1 s}\right)^{2}\left(\sigma_{1 s}^{*}\right)^{2}\left(\sigma_{2 s}\right)^{2}\left(\sigma_{2 s}^{*}\right)^{2}\left(\sigma_{2 p_{z}}\right)^{2}\left(\pi_{2 p_{x}}\right)^{2}\left(\pi_{2 p_{y}}\right)^{2}\left(\pi_{2 p_{x}}^{*}\right)^{2}$

$\left(\pi_{2 p_{y}}^{*}\right)^{1}$

$\mathrm{BO}$ $=\frac{1}{2}\left(\mathrm{~N}_{\mathrm{b}}-\mathrm{N}_{\mathrm{a}}\right)$

$=\frac{1}{2}(10-7)=\frac{3}{2}=1.5$

$\mathrm{O}_{2}^{2-}$ : Total electron $=16+2=18$

Electron configuration in $\mathrm{MO}$ for $\mathrm{O}_{2}^{2-}$ :

$\left(\sigma_{1 s}\right)^{2}\left(\sigma_{1 s}^{*}\right)^{2}\left(\sigma_{2 s}\right)^{2}\left(\sigma_{2 s}^{*}\right)^{2}\left(\sigma_{2 p_{z}}\right)^{2}\left(\pi_{2 p_{x}}\right)^{2}\left(\pi_{2 p_{y}}\right)^{2}\left(\pi_{2 p_{x}}^{*}\right)^{2}$

$\left(\pi_{2 p_{y}}^{*}\right)^{2}$

Bond order of $\mathrm{O}_{2}^{2-}=\frac{1}{2}\left(\mathrm{~N}_{\mathrm{b}}-\mathrm{N}_{\mathrm{a}}\right)$

$=\frac{1}{2}(10-8)=1$

Stability: Bond order increase, as stability increase. The order of stability or under $\mathrm{O}_{2}^{+}(2.5)>\mathrm{O}_{2}(2.0)>\mathrm{O}_{2}^{-}(1.5)>\mathrm{O}_{2}^{2-}(1.0)$

$\longleftarrow$ Bond order and stability increase

Magnetic property : One more unpaired electron, so $\mathrm{O}_{2}, \mathrm{O}_{2}^{+}, \mathrm{O}_{2}^{-}$paramagnetic and in $\mathrm{O}_{2}^{2-}$ all electrons are paired, so $\mathrm{O}_{2}^{2-}$ is diamagnetic.